4 week old Mini Nubian goat with diarrhea..?

It has nothing to do with grass. You caused the scours by not switching him over slowly. Goats are no different than human babies. You cant stop one formula and suddenly start something else. On top of that you went from a powdered replacer that is formulated for goats to milk which has a higher fat content and added corn syrup! Thats a sugar that will draw water to the gut. PLEASE take out the corn syrup and find out what replacer he was on. he should have been transitioned to whole milk very slowly by mixing the formula and milk together over the course of a week. You can very easily kill a kid by suddenly swapping milk like you did.